In all textbooks I used the Diffie-Hellman key exchange is under "public key cryptography".
As far as I can see it is a method to exchange a key to be used with a symmetric cryptographic algorithm, ...

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...

When using symmetric encryption is it important to compress the data first?
I think that compression will make data look "more random" and this might help the ciphertext be harder to crack but I am ...

It seems that quite a few currently available encryption schemes will possibly be broken by quantum computing. Are there any symmetric encryption schemes that will remain unbroken (either because of ...

I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight.
The ...

I have just found a way to crack AES-128 in a reasonable time (1-2 days). How do I publish and prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they ...

I'm developing an application that will use public key authentication to contact some webservice. So the user has his keypair on his computer, and I want that file to be encrypted using AES with a key ...

I work on an exercise and I have to study functions as : $ f : \mathbb{F}_q \rightarrow \mathbb{F}_q$ with $q = 2^n$ which can define a S-Box for SP-Networks.
There is a question that I can't answer ...

A website stores username and password in a session cookie. In the cookie the
password is "encrypted" or modified in some way. Given that the "encrypted"
version is always the same, I do not believe ...

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED!
This might sound really dumb but why is it bad/insecure too use the same key twice on One-time-pad?
Question: Why and how does using ...

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...

Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but ...

I'm attempting to find a client/server authentication protocol that allows the client and server to authenticate each other when the client doesn't know the server secret but does have a sensitive key ...

I am designing a distributed system, composed by a set of physically distributed embedded devices (8 bit cores with less than 1 KB of RAM). The devices need to be able to authenticate the originator ...

Some months ago I found in some paper that we cannot compare symmetric algorithm with asymmetric algorithm based on the key length and more important we cannot compare asymmetric algorithm using only ...

I know using homebrew encryption can be very dangerous as it is very likely to have many flaws in its design. The following concept is just for learning purpose in case anybody is getting red flags ...

To obfuscate data I made up this method on the spot without planning since the goal wasn't real encryption.
At first I though this cannot be real encryption but after revisiting the code and reading ...